Pneumatically operated reversible self-propelled soil penetrating machines for underground hole making are known. Basically these machines comprise a hollow cylindrical body, accommodating a piston-striker and an air distributing mechanism. The front part of the body represents an front anvil with a pointed chisel. A tail nut is screwed in into the rear part of the body, keeping together the components of the air distributing mechanism, the front part of which represents a rear anvil. The air distributing mechanism, comprising controls for forward and reverse modes of operation, causes the piston-striker to reciprocate, imparting significant impacts to the front or to the rear anvil. A machine operation cycle includes a forward and backward stroke of the piston-striker. In the forward mode of operation, the piston-striker at the end of its forward stroke imparts an impact to the front anvil resulting in an incremental body soil penetrating. During the backward stroke, the piston-striker is braked by an air buffer in order to prevent or minimize an impact to the rear anvil. In the reverse mode operation the piston-striker is braked during its forward stroke to eliminate an impact to the front anvil. During the backward stroke the piston-striker imparts an impact to the rear anvil, so that the body moves backward a certain increment of displacement.
Pneumatically operated machines of this type are described in U.S. Pat. Nos. 3,651,874 (3/1972); 3,708,023 (1/1973); 3,727,701 (4/1973); 3,744,576 (7/1973); 3,756,328 (9/1973); 3,865,200 (2/1975); 4,078,619 (3/1978); 4,214,638 (7/1980). The machines according to these patents are characterized by relatively short strokes of the piston-striker, which cause in relatively low impact energy per cycle resulting in high energy consumption at low productivity of the working process. A detailed analysis of these patents is presented in the U.S. Pat. Nos. 5,031,706 and 5,226,487 issued to Spektor (the author of the present invention) in July, 1991 and in July, 1993 respectively.
Analysis of the working process of the existing machines (based on the research investigations, published by the present inventor), shows that the mentioned working process is characterized by relatively high energy consumption at relatively low productivity (average velocity). The theory of minimization of energy consumption of soil working cyclic processes, developed and published by the present inventor, indicates that the process of vibratory soil penetration can be optimized with respect to minimum energy consumption. (See: Minimization of Energy Consumption of Soil Deformation, Journal of Terramechanics, 1980, Volume 17, No. 2, pages 63 to 77; Principles of Soil-Tool Interaction, Journal of Terramechanics, 1981, Volume 18, No. 1, pages 51 to 65; Motion of Soil-Working Tool Under Impact Loading, Journal of Terramechanics, 1981, Volume 18, No. 3, pages 133 to 136; Working Processes of Cyclic-Action Machinery for Soil Deformation--Part I, Journal of Terramechanics, 1983, Volume 20, No. 1, pages 13 to 41; Minimum Energy Consumption of Soil Working Cyclic Processes, Journal of Terramechanics, 1987, Volume 24, No. 1, pages 95 to 107). These investigations indicate that in order to optimize the working process, the impact energy of the striker should be significantly increased, which can be achieved with a long stroke air distributing mechanism. Following the outcome of these investigations, the author developed a differential pneumopercussive reversible self-propelled soil penetrating machine, which is characterized by a long stroke air distributing mechanism. This machine is described in the U.S. Pat. No. 5,311,950 issued to Spektor (the author of the present invention) in May, 1994. According to this patent, the machine includes, as major assemblies, an elongated compound housing assembly, comprising an outer tube which concentrically accommodates an inner tube creating a tubular space between these tubes; a striker assembly disposed for reciprocation within the inner tube; a front anvil assembly rigidly secured to the front part of the inner tube comprising an elastic link and a chisel; a rear anvil assembly rigidly secured to the inner tube rearwardly of the striker assembly; a differential valve-operated air distributing mechanism secured in the inner tube rearwardly of the rear anvil assembly; and a tail nut assembly for securing together the outer and inner tubes and keeping in place the air-distributing mechanism.
The testing of the machine described in the U.S. Pat. No. 5,311,950 has demonstrated positive results, however the engineering analysis of this machine shows several structural disadvantages which decrease the efficiency of the machine and increase its cost.
The most essential disadvantage is associated with the structure of the compound housing comprising the outer and inner tubes. First of all, the mass of this housing is relatively much bigger than the mass of the striker which results in a relatively low efficiency transfer of impact energy from the striker to the housing. Secondly, the summarized wall thickness of these two concentric tubes causes a relatively significant decrease in the diameter of the striker, and , consequently, the pressure force is respectively reduced, resulting in a relatively low impact energy per cycle for the given outside diameter of the machine. All this does not allow to obtain a relatively high efficiency of the machine performance. Thirdly, the components for keeping the tubes concentrically and also the longitudinal elastic strips, located between the tubes, increase the manufacturing cost and complexity of the machine.
Another disadvantage of the considered machine is related to the tail nut assembly, which may become loose, and then cause the termination of the functioning of the machine. The components of this assembly also increase the manufacturing cost and the complexity of the machine.
A further disadvantage of the considered machine is associated with the complexity of the front anvil assembly and low durability of the elastic diaphragm of this assembly which result in increasing of the cost of manufacturing and maintenance of the machine.
Still another inherent disadvantage of the considered machine as well as all other similar existing machines is the absence of means for directional stability of the machine which may cause in an unacceptable deviation of the trajectory of the machine.
One more inherent disadvantage of conventional underground pneumopercussive hole making machines is lack of means or methods of retracting from the hole a machine by the help of another identical or similar machine in case of quitting of the air-distributing mechanism of the first machine due to a failure of a barb, hose, connector, etc.
The present invention eliminates all these disadvantages, offering a machine, characterized by significantly increased efficiency at lower complexity and manufacturing cost.
The new structural solution of the present invention is incorporated in many full scale prototypes that have been successfully tested in laboratory and field conditions. The results of the extensive testing of these prototypes confirm an essential improvement of their performance in comparison with the considered machine. In addition to this, the reliability of the prototypes is significantly increased while their manufacturing and maintenance cost is essentially reduced.